The present invention concerns fluid condition controlled mixing valves. In particular, the invention concerns a mixing valve responsive to varying fluid conditions, such as temperature, to maintain a desired stable fluid condition. The invention also concerns a bypass mechanism which provides a constant flow of fluid when the desired condition cannot be achieved.
Thermally controlled or thermostatic mixing valves are well known. Many such fluid mixing valves include a single control knob that can be rotated to vary the temperature of the output fluid between off, cold and hot positions. The valve member is controlled by a thermally responsive control member, or a thermostat, to maintain the fluid temperature according to the setting of the control knob. Thermally operated mixing valves are frequently used to control the temperature water through a shower fitting. Other applications include an emergency eye-wash fountain in which tepid water is providing for washing the eyes of a victim of some contamination. In both cases, it is important the mixing valve properly operate to maintain the pre-set temperature of the flow of liquid from the valve. In many cases, the mixing valve maintains the temperature of the output liquid to within plus or minus 2.degree. F. of the preset temperature.
In an application of mixing valves in which the output fluid is in contact with the user, it is critical that some form of emergency shut-off be provided in the event of a failure of at least the cold fluid source. In the absence of such an emergency mechanism, the user may be scalded by the hot water flowing exclusively through the valve in the absence of cold mixing water, during the lag before the thermostat functions to shut the valve off. In other applications, such as the eye-wash application, it is also important that the mixing valve has some means for maintaining some flow of liquid through the valve in the event of a failure of the valve or thermal control member. In the eye-wash application, it is imperative that at least some cold water is maintained, otherwise the victim may suffer serious injury for failure to wash the eyes completely. U.S. Pat. No. 5,011,074 to the present inventor teaches a thermostatic mixing valve with a thermostatic failure compensation means. In the event of a failure of the thermostat, the invention operates to prevent hot flow into the mixing chamber.
In other applications of mixing valves, such as in combination with carbonated beverage dispensers, it is desirable to provide a fluid with a desired temperature. Fluid from a chiller is mixed with room-temperature (warm) fluid to achieve a desired temperature. This temperature controlled fluid is fed to a carbonator such as may be found in a commercial soda machine or carbonated beverage dispenser.
However, if the chiller is not properly maintained, the chiller or the lines from the chiller may become clogged with ice. When this occurs, a prior art thermostatic mixing valve would operate to shut down the output of fluid because the thermostat, sensing only warm fluid would try to feed more cold and less warm fluid. A prior art mixing valve would regulate the relative flow volume of a warm fluid versus the flow volume of a relatively chilled into the mixing chamber fluid in order to maintain a constant temperature of the output fluid. If the flow of the chilled fluid ceased, the temperature in the mixing chamber would therefore increase and the thermostat and the mixing valve would react to restrict or stop the input of the warm fluid. This would lead to substantial decrease in or complete cessation of fluid output, which is unacceptable in commercial applications, such as fast food restaurants. The present invention provides a thermostatic mixing valve with a bypass mechanism that ensures a room temperature product fluid in the absence of chilled fluid. The valve, in essence, frustrates the normal function of a thermostatic valve when a flow of fluid ceases.